Vastus lateralis muscle biopsies have been collected from all of the squirrel monkeys. The samples were frozen for processing. Biochemical and histological analysis of the muscle samples is complete and the data are being analyzed. Assays include myosin ATPase activity for determination of muscle fiber type, proportions, and cross-sectional area. Preliminary data indicate an age-related decline in type II fibers, consistent with other species. A grip strength apparatus was developed and monkeys are currently being trained to use it. Preliminary data show an decrease in grip force with age. Grip force will provide a functional measure of muscle strength and an approximation of maximal grip force. A CT scan was performed on two squirrel monkeys to assess the feasibility of using this technology to assess body composition. We determined that calculation of whole body lean mass would be difficult to determine but the effect of an intervention on changes in lean mass in the legs may be possible.